Inductive power supply with device identification

ABSTRACT

An inductive power supply system to identify remote devices using unique identification frequencies. The system includes an AIPS and a tank circuit capable of inductively providing power to a remote device at different frequencies, and a sensor for sensing the reflected impedance of the remote device at tank circuit. The system further includes a plurality of different remote devices, each having a unique resonance frequency. In operation, the AIPS is capable of identifying the type of remote device present in the inductive field by applying power to a remote device at a plurality of unique identification frequencies until the remote device establishes resonance in response to one of the identification frequencies. The AIPS includes a controller that recognizes when resonance has been established by evaluating sensor data, which is representative of the reflected impedance of the remote device. Once the identity of a remote device is determined, the AIPS may pull operating parameters for the remove device from memory to ensure efficient operation and to assist in recognizing fault conditions.

The present invention relates to inductive power supply systems, andmore particularly to an apparatus and method for inductive powering avariety of alternative remote devices.

There is a significant and continually increasing interest in wirelesspower supply systems, particularly in the field of consumer and businesselectronics, such as cell phones, music players, personal digitalassistants and other remote devices. Wireless power supply systemsprovide a variety of benefits over conventional wired connections. Mostnotably, they eliminate the need for various charging cords and the needto repeatedly plug in and unplug electronic devices for recharging,thereby reducing cost and improving ease and convenience of use.

Systems for providing wireless power using the principles ofelectromagnetic inductive have been available for many years.Conventional systems have met with limited success as a result ofpractical limitations on pre-existing inductive technology. For example,to provide reasonably efficient operation, conventional inductivesystems typically require close and precise alignment between theprimary coil and the secondary coil, as well as a high degree ofcoordinated tuning between the electronics in the inductive power supplyand the electronics in the remote device. These problems are complicatedby the fact that different remote devices typically operate withindifferent parameters. For example, one cell phone model is likely tohave a different set of operating parameters than a different cell phonemodel, and even greater differences are likely to exist between remotedevices of different types, such as a cell phone and a music player.

U.S. Pat. No. 6,825,620 to Kuennen et al discloses an inductive powersupply system that has the ability to adjust its operation to correspondwith the operating parameters of various loads. U.S. Pat. No. 6,825,620to Kuennen et al, which is entitled “Inductively Coupled BallastCircuit” and was issued on Nov. 30, 2004, is incorporated herein byreference. This inductive power supply system is capable of efficientlypowering a wide variety of loads. Although a marked improvement overpre-existing systems, there is, in some applications, a desire for evengreater efficiency over a broader range of products using a singleinductive power supply system. In some applications, there exists adesire for a single inductive power supply that is capable of making adistinction between different loads, based upon various operatingparameters of those loads. In other applications, there also exists adesire for a single inductive power supple system capable of morereadily recognizing fault conditions over a broad range of remotedevices.

SUMMARY OF THE INVENTION

The present invention provides an inductive power supply system andassociated method in which an adaptive inductive power supply (“AIPS”)identifies the remote device through reflected impedance, and controlsoperation as a function of the identity of the remote device. Thepresent invention also provides the AIPS with the ability to assessfault conditions by recognizing when the secondary circuit is operatingoutside of normal operating conditions for the identified device.

In one embodiment, the present invention includes an AIPS having acontroller capable of supplying power to the secondary circuit atvarious frequencies and a current sensor capable of directly orindirectly sensing the current in the tank circuit. In this embodiment,each remote device or type of remote device includes one or moreresonant frequencies that individually or collective provide a signaturethat is unique to that device or type of remote device. For example, theidentification frequency(ies) may uniquely identify a specific model ofcell phone or a specific model of personal digital assistant. The systemmay also include a look-up table or other data collection containingoperating information for one or more recognizable remote devices. Thisinformation can be used to establish operating parameters and recognizefault conditions.

In operation, the AIPS applies a short pulse of power to the secondarycircuit at a frequency that is uniquely associated with a specificremote device. If the remote device has a resonant frequency at thefrequency of the pulse, the remote device will draw a material amount ofcurrent, which will be reflected back into the tank circuit throughreflected impedance. The controller will recognize the presence of theremote device when input from the current sensor shows the increasedpower draw. This permits the AIPS to recognize that a specific remotedevice is present and to obtain its operating parameters from thelook-up table. Once the operating parameters have been retrieved, theAIPS can use the retrieved parameters to more efficiently power thedevice and to recognize that a fault condition has occurred when actualoperating conditions fall outside the retrieved operating parameters.

In some applications, the remote device may inherently include aresonant frequency (or plurality of resonant frequencies) that issufficiently unique to permit it to function as an identificationfrequency. In such application, the remote device will operate atresonance when the corresponding identification frequency is applied,thereby uniquely identifying the remote device.

In other applications, the remote device may not inherently have aresonant frequency at a frequency that will uniquely identify the removedevice. With remote devices of this nature, the remote device can beprovided with an identification capacitor that is selected to providethe remote device with a unique resonant frequency (or pattern offrequencies) that can be identified using an identification ping. Insome applications, the main circuitry of the remote device may mask theidentification capacitor. Accordingly, in some applications, the remotedevice may include a load delay circuit that isolates the main circuitof the remote device from the secondary coil and the identificationcapacitor for a sufficient period of time to allow resonance to beestablished by the identification capacitor and reflected back to thetank circuit.

In applications where the number of potential remote devices is large, aplurality of capacitors may be used to provide the remote devices with aplurality of resonant frequencies that collectively provide each remotedevice with a unique resonant “signature” in response to pings atdifferent frequencies. For example, the use of two different capacitorscan be used to provide three separate resonant frequencies-one for eachcapacitor individually and a third for the combination of the twocapacitors. In one embodiment, the presence or absence of resonance atselect frequencies can be used as the bits in a binary code that canunique identify a large number of remote devices with only a limitednumber of frequencies.

In one embodiment, the method generally includes the steps of applying ashort pulse of power to the secondary circuit at an identificationfrequency, waiting a period of time and sensing the current in the tankcircuit to determine if a remote device is present that has a resonantfrequency at the frequency of the short pulse of power. If so, theremote device is identified and the operating parameters can be pulledfrom a lookup table or other memory device. If not, the AIPS can move tothe next identification frequency and repeat the process. In someapplications, a small delay may be implemented between eachidentification ping to allow the circuit to settle so that residualenergy from one identification ping does not impact the remote device'sresponse to the next identification ping. The system may repeatedlycycle through all of the possible identification frequencies until aremote device is positively identified.

In another embodiment, each remote device capable of being powered by aninductive power supply is provided with a capacitor with the same commonresonant frequency. The inductive power supply is programmed to send ashort power pulse at that single common resonant frequency. A responsefrom the device, as described above, indicates that the device iscapable of receiving power from the power supply.

In another embodiment, each device capable of being powered by aninductive power supply is equipped with a capacitor with a commonresonant frequency, and one or more additional capacitors with uniquesecondary and/or tertiary resonant frequencies. According to thisembodiment, the inductive power supply is programmed to send a shortpower pulse at the single common resonant frequency. When the supplysenses a response at that frequency, the inductive power supply sendsout additional short pulses at different frequencies, or over a range offrequencies. Depending on the responses at the various frequencies, thepower supply is able to distinguish the type of device, and the specificdevice model.

Once a remote device has been identified, the AIPS can provide power tothe remote device in accordance with the operating parameters pulledfrom memory. Additionally, the AIPS can use information from the lookuptable to help identify fault conditions. For example, the lookup tablecan include minimum and maximum operating frequencies, as well asminimum and maximum current usage. If the current draw on the primaryexceeds the maximum current retrieved from the lookup table, the AIPSwill recognize a fault condition and take appropriate action, such aspowering down the primary.

The present invention provides a simple and effective method andapparatus for identifying remote devices. The lookup table permits theAIPS to retrieve information regarding the remote devices, such asnormal operating parameters. This allows the AIPS to more efficientlypower the remote device and to more readily identify fault conditions.In applications where a single resonant frequency does not provide asufficient number of unique identifications, each device may be providedwith a pattern of identification frequencies. In applications where aremote device inherently includes a uniquely identifying resonantfrequencies (or frequency pattern), the present invention requires nomodification to the remote device. In applications where a remote devicedoes not include an inherent uniquely identifying resonant frequency,the remote device may be provide with one or more identificationcapacitors that provide the remote device with an identificationfrequency or an identification frequency pattern. In another aspect, thepresent invention provides a set of standards from which a class ofremote devices may be identified by predetermined identificationfrequencies. This permits intelligent operation of the AIPS for anessentially unlimited numbers of remote devices that fit within one ofthe predetermined classes of remote devices.

These and other objects, advantages, and features of the invention willbe readily understood and appreciated by reference to the detaileddescription of the current embodiment and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an inductive power supply system inaccordance with an embodiment of the present invention.

FIG. 2 is a circuit diagram of the inductive power supply system of oneembodiment.

FIG. 3A is a circuit diagram of an alternative remote device having anidentification capacitor.

FIG. 3B is a circuit diagram of an alternative remote device having aplurality of identification capacitors.

FIG. 4 is a circuit diagram of a second alternative remote device.

FIG. 5 is a table showing various capacitor values and associatedresonant frequencies available from select capacitor combinations.

FIG. 6 is a flow chart showing the general steps of a method foridentifying a remote device.

DESCRIPTION OF THE CURRENT EMBODIMENT

An inductive power supply system in accordance with an embodiment of thepresent invention is shown in FIG. 1. The inductive power supply system10 generally includes an adaptive inductive power supply (“AIPS”) 12 andone of a plurality of remote devices 14. The AIPS 12 generally includesa tank circuit 48 with a primary coil 18 (See FIG. 2) capable ofinductively transmitting power. The AIPS also includes a controller 20for selectively controlling the frequency at which power is generated bythe primary coil 18, and a sensor 16 capable of sensing reflectedimpedance from a remote device 14. The AIPS 12 is intended for use withone or more remote devices 14, each of which has a unique resonantfrequency or unique pattern of resonant frequencies. In operation, theAIPS 12 applies power to the primary 18 at an identification frequencyand then evaluates the reflected impendence of the remote device 14using the current sensor 16. If the remote device 14 has a resonantfrequency at the identification frequency, then the AIPS 12 knows whattype of remote device is inductively coupled to AIPS 12 and the AIPS 12can recover operating parameters from a look-up table or other memorydevice. The recovered information can be used by the AIPS to provideefficient operation of the remote device and to identify faultconditions.

I. Adaptive Inductive Power Supply.

The present invention is suitable for use with a wide variety ofadaptive inductive power supplies. As used herein, the term “adaptiveinductive power supply” is intended to broadly include any inductivepower supply capable of providing power at a plurality of differentfrequencies. For purposes of disclosure, the present invention isdescribed in connection with a particular AIPS 12. The illustrated AIPS12 is merely exemplary, however, and the present invention may beimplemented with essentially any AIPS capable of providing inductivepower at varying frequencies.

In the illustrated embodiment, the AIPS 12 generally includes afrequency controller 20 and a tank circuit 48. In operation, thefrequency controller 20 applies power to the tank circuit 48 to generatea source of electromagnetic inductive power. The frequency controller 20of the illustrated embodiment generally includes a microcontroller 40,an oscillator 42, a driver 44 and an inverter 46. The microcontroller 40may be a microcontroller, such as a PIC18LF1320, or a more generalpurpose microprocessor. The oscillator 42 and driver 44 may be discretecomponents or they may be incorporated into the microcontroller 40, forexample, in the embodiment illustrated in FIG. 2, the oscillator 42 is amodule within the microcontroller 40. The frequency controller 20 mayalso include a low voltage power supply 26 for supplying low voltagepower to the microprocessor 40 and the driver 44. In this embodiment,the various components of the frequency controller 20 collectively drivethe tank circuit 48 at a frequency dictated by the microcontroller 40.More specifically, the microcontroller 40 sets the timing of theoscillator 42. In certain modes of operation, the microprocessor 40 mayestablish the operating frequency as a function of input from thecurrent sensor 16. The oscillator 42, in turn, operates the driver 44 atthe frequency established by the microcontroller 40. The driver 44provides the signals necessary to operate the switches 47 a-b within theinverter 46. As a result, the inverter 46 provides AC (alternatingcurrent) power to the tank circuit 48 from a source of DC (directcurrent) power 50.

In the illustrated embodiment, the current sensor 16 is a currenttransformer having its primary coil disposed in the tank circuit 48 andits secondary coil connected to the microcontroller 40. The AIPS mayinclude conditioning circuitry 28 for conditioning the currenttransformer output before it is supplied to the microcontroller 40.Although the illustrated embodiment includes a current transformer forsensing the reflected impedance of the remote device, the AIPS 12 mayinclude essentially any alternative type of sensor capable of providinginformation regarding reflected impedance from the remote device 14.Further, although the current sensor 16 of the illustrated embodiment islocated in the tank circuit, the current sensor (or other reflectedimpedance sensor) can be located in essentially any location where it iscapable of providing readings indicative of the presence or absence ofresonance in the remote device.

In the illustrated embodiment, the AIPS further includes a lookup table24 or other memory device capable of storing information relating to theoperating parameters of a plurality of remote devices 14. The storedinformation may be used to permit the AIPS 12 to more efficiently powerthe remote device 14 and more readily recognize fault conditions. Insome applications, the AIPS 12 may be intended for use with a specificset of remote devices 14. In these applications, the lookup table 24includes the unique resonant frequency (or pattern of frequencies) foreach remote device 14, along with the desired collection of associatedinformation, such as maximum and minimum operating frequencies andcurrent usage. The lookup table 24 may, however, include essentially anyinformation that may be useful to the AIPS 12 in operating the remotedevice 14. For example, in applications where it is desirable toestablish wireless communications with the remote device 14, the lookuptable 24 may include information regarding the wireless communicationprotocol of the remote device 14.

The tank circuit 48 generally includes the primary coil 18 and acapacitor 52. The capacitance of capacitor 52 may be selected to balancethe impedance of the primary coil 18 at anticipated operatingparameters. The tank circuit 48 may be either a series resonant tankcircuit (as shown) or a parallel resonant tank circuit (not shown). Thepresent invention may be incorporated into the AIPS shown in U.S. Pat.No. 6,825,620, which as noted above is incorporated herein by reference.As another example, the present invention may be incorporated into theAIPS shown in U.S. Patent Application Publication US 2004/130916A1 toBaarman, which is entitled “Adapted Inductive Power Supply” and waspublished on Jul. 8, 2004 (U.S. Ser. No. 10/689,499, filed on Oct. 20,2003), which is also incorporated herein by reference. Further, it maybe desirable to use the present invention in connection with an AIPScapable of establishing wireless communications with the remote device,such as the AIPS shown in U.S. Patent Application Publication US2004/130915A1 to Baarman, which is entitled “Adapted Inductive PowerSupply with Communication” and was published on Jul. 8, 2004 (U.S. Ser.No. 10/689,148, filed on Oct. 20, 2003), which is incorporated herein byreference.

II. Remote Devices.

The present invention is intended for use with a wide variety of remotedevices of varying designs and constructions. It is anticipated thatthese various remote devices will require power at varying frequency andwill have different current requirements.

In some applications, the remote device may inherently include a uniqueresonant frequency or pattern of resonant frequencies. For example, aspecific type of remote device may include a resonant frequency at 195kHz. If none of the other remote devices to be identified by the AIPSinclude a resonant frequency at 195 kHz, then 195 kHz can operate as theidentification frequency for this type of remote device. On the otherhand, if the remote device does not include a resonant frequency that isunique among the set of remote devices that may need to be identified,then it may be possible to use the presence of a unique pattern ofresonant frequencies to identify the remote device. For example, aremote device may have one resonant frequency at 195 kHz and anotherresonant frequency at 215 kHz. Even if other remote devices have aresonant frequency at 195 kHz or at 215 kHz, the combination of the tworesonant frequencies in a single type of remote device may be sufficientto uniquely identify the type of remote device. If two resonantfrequencies are not sufficient to uniquely identify a type of remotedevices, then even more resonant frequencies may be considered until aunique pattern of identification frequencies emerges.

For purposes of disclosure, one embodiment of a remote device 14 havingan inherent identification frequency is shown in FIG. 2. In theembodiment of FIG. 2, the remote device 14 generally includes asecondary 22 for receiving power from the AIPS 12, a bridge 30 (or otherrectifier for converting AC power to DC), a charging circuit 32, abattery 34 and a main circuit 36. In operation, the bridge 30 convertsthe AC power generated in the secondary 22 to DC power, which isrequired for operation of charging circuit 32 in this embodiment.Charging circuits are well-known and are widely used with a variety ofrechargeable electronic devices. If desired, the charging circuit 32 maybe configured to both charge the battery 34 and/or power the remotedevice 14 (if the remote device 14 is powered on). Charge circuitscapable of charging and/or powering an electronic device are well-knownand therefore will not be described in detail. In some applications, thecharging circuit 32 will be a part of the main circuit 36. In otherapplications, the charging circuit 32 will be a separate circuit, andmay even be controlled by the AIPS 12, if desired. The term “maincircuit” is used loosely to refer to the operating circuitry for theremote device 14.

Although the illustrated embodiment is described in connection with abattery-powered remote device, the present invention may alternativelybe used to directly power a remote device by eliminating the battery 34and charging circuit 32 and connecting the secondary 22 to the maincircuit 36, for example, through appropriate power conditioningcircuitry, which may include a transformer or rectifier (such as bridge30).

In another embodiment, a remote device may be provided with one or moreidentification capacitors that provide resonance at desiredidentification frequencies. Although useable with all remote devices,this embodiment is perhaps most useful with remote devices that do nothave an inherent identification frequency or inherent identificationpattern of frequencies. FIG. 3A shows a circuit diagram of an exemplaryremote device 14′ having an identification capacitor 38′. As shown inFIG. 3A, an identification capacitor 38′ is connected in parallel acrossthe secondary 22′. The identification capacitor 38′ has a capacitanceselected to establish resonance at the identification frequency. In thisembodiment, it is possible that the charging circuit 32′ and/or the maincircuit 36′ will mask the identification capacitor 38′ making itdifficult or impossible for the AIPS 12 to recognize the presence of theidentification capacitor 38′. Accordingly, in this embodiment, theremote device 14′ includes a load enable delay circuit 54′ that preventsthe charging circuit 32′ and/or the main circuit 36′ from receivingpower for a period of time sufficient for the identification capacitor38′ to establish resonance and for that resonance to be conveyed to theAIPS 12 through reflected impedance. The load enable delay circuit 54′may include a simple timed switching circuit that connects the bridge30′ to the charging circuit 32′ only after a sufficient period of timehas lapsed. This embodiment is particularly well-suited forincorporating the present invention into remote devices alreadyincluding a charging circuit. FIG. 4 shows an alternative embodimentintended primarily for use in incorporating the present invention intoremote devices not already including charging circuitry or that includecharging circuitry having a microprocessor with an enable input. In thisembodiment, the load enable delay 54′″ is connected to the “enable”input of the microprocessor in the charging circuitry 32′″. In thisembodiment, the load enable delay 54′″ does not enable the chargingcircuitry 32′″ until a sufficient amount of time has passed for the AIPS12 to recognize whether or not the identification capacitor 38′″ hasestablished resonance. Although described in connection with twospecific embodiment, the load enable delay circuit may be essentiallyany circuitry capable of preventing the charging circuit and/or maincircuit from masking the identification capacitor long enough for theAIPS 12 to recognize whether resonance has been established.

In the embodiment of FIG. 3A, the remote device 14′ includes only asingle identification capacitor 38′. In the embodiment shown in FIG. 3B,the remote device 14″ is provided with three identification capacitors38 a-c″ connected in parallel to the load each providing resonance at adifferent frequency. In a similar manner, additional identificationcapacitors can be provided to establish even more additional resonantfrequencies, if desired. For example, FIG. 5 is a table showing theresonance frequencies that may be provided using different combinationsof four capacitors. The first four columns labeled C1-C4 list thecapacitance (in microfarads) of four different capacitors. In thisexample, the capacitors are 8.2, 6.8, 3.3, and 2.2 microfaradcapacitors. The capacitors used in this table or merely exemplary andare not intended to limit the scope of the present invention. The secondfour columns labeled C1-C4 identify the capacitors included thatparticular combination, using a “1” to represent the presence of acapacitor and a “0” to represent the absence of a capacitor. The columnlabeled “Capacitance” provides the combined capacitance of thecapacitors in that particular combination. The column labeled“Frequency” provides the resonant frequency of the capacitor combinationwhen the inductance is 0.000000309 as specified in the last column. Forexample, row four includes a “1” in the C1 and C2 columns to indicatethat an 8.2 microfarad capacitor and a 6.8 microfarad capacitor arecombined to provide a combined capacitance of 3.7173 microfarad, whichwill have a resonant frequency of roughly 148.5 kHz. In addition to theresonant frequency created by the combined capacitance of the twocapacitors, the identification capacitors will also establish resonanceat the individual capacitances of each capacitor in that combination.So, continuing with the row 4 example, the combined capacitors will alsohave a resonant frequency at roughly 100 kHz (the resonance frequency ofthe 8.2 microfarad capacitor) and at roughly 109.9 kHz (the resonancefrequency of the 6.8 microfarad capacitor). As can be seen, thecombination of 8.2 and 6.8 microfarad capacitors provides anidentification frequency pattern with resonance at roughly 100 kHz,109.9 kHz and 148.5 kHz.

The particular remote devices described above are merely exemplary asthe present invention is well-suited for use with essentially any remotedevice having an identification frequency and capable of inductivelyreceiving power within the limits of the AIPS.

III. Operation.

General operation of the system 10 is described in connection with FIG.6. In this embodiment, the system 10 is configured to recognize one of aplurality of remote devices. Each remote device includes a singleresonant frequency that is unique among the remote devices. Accordingly,the AIPS 12 can uniquely identify a remote device by cycling througheach of the potential identification frequencies until a remote deviceis present that establishes resonance at one of the potentialidentification frequencies.

In the illustrated embodiment, the AIPS 12 is provided with datadefining a plurality of potential identification frequencies. Forexample, a list or table of potential identification frequencies may bestored in onboard memory on the microcontroller 40. The identificationprocess begins by setting 100 the identification frequency to the firstfrequency in the list. The AIPS 12 then applies 102 power to the tankcircuit 48 at the identification frequency. The AIPS 12 continues toapply power to the tank circuit 48 for a period of delay 104. The delayperiod is selected to provide sufficient time for the remote device 14to establish resonance and to generate sufficient reflected impedance inthe tank circuit 48. The delay period may be a fixed period of time thatremains constant throughout the identification process. The delay periodmay vary from application to application, but in the illustratedembodiment is approximately 6 microseconds. In some applications, asufficient delay may be inherent in the system and therefore may notrequire the implementation of a separate deliberate delay step. If theremote device 14 includes a resonant frequency at the identificationfrequency, the remote device 14 will draw current and this increase incurrent draw will be reflected back into the tank circuit 48 byreflected impedance. After the delay 104 is complete, the microprocessor40 obtains 106 input from the current sensor 16. As noted above, theoutput of the current sensor 16 may be conditioned using conditioningcircuitry 28. The microprocessor 40 evaluates the input from the currentsensor 16 to determine whether the remote device 14 has a resonantfrequency at the current identification frequency. In this embodiment,the microprocessor 40 will conclude that a resonant frequency exists ifthe current sensor reading is above a threshold value. Typically, thethreshold value for a specific application will be a value above thenoise floor of that application plus an additional deadband. The amountof the deadband may vary from application to application.

If the microprocessor 40 determines that the remote device 14 does notinclude a resonant frequency at the current identification frequency,then the controller 20 prepares to apply to the next identificationfrequency to the tank circuit 48. More specifically, the microprocessor40 enters a delay 114 for a relatively short period of time. The delayperiod is selected to provide sufficient time for the remote device 14to settle and for the energy in the remote device 14 to sufficientlydissipate. The delay period may be a fixed period of time that remainsconstant from throughout the identification process. The settle delayperiod may vary from application to application, but in the illustratedembodiment is approximately 5 microseconds. In some applications, asufficient delay may be inherent in the system and therefore may notrequire the implementation of a separate deliberate settle delay step.After the delay, the microprocessor 40 sets the identification frequencyas the next frequency in the list of potential identificationfrequencies. The process then repeats beginning with the step ofapplying 102 power to the tank circuit 48 at the new identificationfrequency.

If the microprocessor 40 determines that the remote device 14 includes aresonant frequency at the current identification frequency, themicroprocessor 40 will retrieve 110 the operating parameters from thelookup table 24 and will exit the remote device identification process.The microprocessor 40 may then operate 112 the remote device 14 usingthe operating parameters retrieved from lookup table 24. The lookuptable 24 may include an anticipated operating frequency and may beginoperation by applying power to the tank circuit 48 at the recalledoperating frequency. The microprocessor 40 may also use maximum andminimum current draws values obtained from the lookup table to determinethe presence of a fault condition. For example, if during operation theactual current draw sensed by the current sensor exceeds the maximumcurrent draw or falls below the minimum current draw, the microprocessor40 will conclude that a fault condition exists. The microprocessor 40may be programmed to take remedial action if a fault condition isencountered. For example, the microprocessor 40 may be programmed toshut down the system if a fault condition arises. Alternatively, themicroprocessor 40 may restart the identification process to determine ifa different remote device 40 has been placed near the primary 18.

In the embodiment described above, the microprocessor 40 cycles througha list of potential identification frequencies in an effort to identifya remote device. As an alternative to cycling through a list, the AIPS12 may be programmed to simply cycle through a range of frequenciesusing a specified step value. For example, by stepping from 100 kHz to300 kHz in 5 kHz increments.

In another aspect, the present invention provides a mechanism forestablishing standards for using frequency identification for remotedevices. In this embodiment, unique identification frequencies can bespecified for each type of remote device and for other identifyingfeatures. For example, the standards may specify a differentidentification frequency for each type of device (e.g. cell phone,personal digital assistant, may digital music player) and/or for eachmanufacturer (e.g. company name). In applications where a uniqueidentification frequency is assigned to each manufacturer, themanufacturer may be permitted to add additional identificationfrequencies to specify model numbers and product types.

In an alternative method for establishing standards, identificationfrequencies can be establish by the class of the remote device ratherthan the specific model type. For example, all devices operating withina given set of operating parameters can be assigned the sameidentification frequency (or identification frequency pattern). Thisalternative method is particularly well-suited for use in applicationwhere a plurality of remote devices of different types are capable ofoperating under the operating parameters set forth in a single record inthe lookup table.

According to another embodiment, each device capable of beinginductively powered or charged by an inductive power supply is providedwith at least one common resonant frequency, and at least one uniquefrequency. For example, referring to the above embodiments and thefigures, each device capable of being charged by AIPS 12 is providedwith an 8.2 microfarad capacitor, providing the device with a primaryidentification resonant frequency of 100 kHz. AIPS 12 repeatedly sendsout a pulse at approximately 100 kHz. If a device 14 with a resonantfrequency of 100 kHz is placed within the field generated by AIPS 12,then AIPS proceeds with a sweep of additional frequencies to identifythe type of device 14. According to one embodiment, the charging circuitof each individual battery type is provided with a second uniqueresonant frequency, or secondary identification frequency. For example,each lithium ion battery is further comprised of a capacitor or othercircuitry to provide a secondary resonant frequency at 109.4 kHz; eachnickel cadmium battery is provided with a capacitor or other circuitryto provide a secondary resonant frequency at 148.5 kHz. According toanother embodiment, each battery may further equipped with a capacitoror other circuitry to provide a tertiary resonant frequency used toidentify the individual manufacturer or supplier of that battery. Forexample, each inductively charged lithium ion battery manufactured orsold by vendor X is provided with one or more capacitors or othercircuitry to provide a primary identification resonant frequency of 100kHz, a secondary identification resonant frequency of 109.4 kHz, and atertiary identification resonant frequency of 130 kHz. Each lithium ionbattery manufactured or sold by vendor Y is provided with one or morecapacitors or other circuitry to provide a primary identificationresonant frequency of 100 kHz, a secondary identification resonantfrequency of 109.4 kHz, and a tertiary identification resonant frequencyof 140 kHz. According to another embodiment, an additionalidentification resonant frequency may be added to distinguish, forexample, different types of inductively charged lithium ion batteriessold by vendor X or vendor Y. Such identification could allow AIPS toadjust the charging or power control not only according to therequirements of various load types as discussed above, but according tospecific requirements of individual manufacturers or suppliers of thoseload types. It would be obvious that such identification strategies andprotocols could be used to identify inductive loads that are not onlypowered by a rechargeable battery, but also to identify those loads thatare directly inductively powered.

The standards discussed above rely on the assignment of a range ofidentification frequencies. The spacing between identificationfrequencies may vary from application to application depending of theresolution of the AIPS sensing the present of resonance during theidentification process. For example, an AIPS with sufficient resolutionto accurately recognize frequency differences of 5 kHz can use aseparation of 5 kHz between identification frequencies (e.g. 250 kHz and255 kHz). An AIPS with lower resolution may require greater separationbetween identification frequencies (e.g. 250 kHz and 260 kHz).

The above description is that of current embodiments of the invention.Various alterations and changes can be made without departing from thespirit and broader aspects of the invention as defined in the appendedclaims, which are to be interpreted in accordance with the principles ofpatent law including the doctrine of equivalents. Any reference to claimelements in the singular, for example, using the articles “a,” “an,”“the” or “said,” is not to be construed as limiting the element to thesingular.

1. A method for controlling an inductive power supply, comprising thesteps of: associating an identification frequency with a remote device,the identification frequency including at least one frequency at whichthe remote device has a resonant frequency; applying an inductive fieldto a remote device at the identification frequency; determining whetherthe remote device has a resonant frequency substantially at the appliedidentification frequency; and operating the inductive power supply basedon an outcome of said determining step.
 2. The method of claim 1 whereinsaid operating step is further defined as the steps of: retrieving atleast one parameter for the remote device from a memory associated withthe inductive power supply, if the remote device has a resonantfrequency substantially at the applied identification frequency; andafter said retrieving step, operating the inductive power supply toapply power to the remote device in accordance with the parameter. 3.The method of claim 2 further including the step of storing in memory atleast one parameter for the remote device associated with theidentification frequency.
 4. The method of claim 3 wherein saidassociating step is further defined as associating a plurality ofdifferent identification frequencies with a plurality of differentremote devices; and wherein said applying step and said determining stepare repeated for each of the different identification frequencies untilthe remote device is determined to have a resonant frequencysubstantially at the applied identification frequency.
 5. The method ofclaim 4 wherein said storing step is further defined as storing inmemory at least one parameter for each of the plurality of differentremote devices.
 6. The method of claim 5 further including the step ofactively configuring each of the plurality of remote devices to includea resonant frequency at a desired unique frequency, the identificationfrequency including the resonant frequency, whereby each of saidplurality of remote devices may be uniquely identified by itscorresponding identification frequency.
 7. The method of claim 5 furtherincluding the step of actively configuring each of the plurality ofremote devices to include a plurality of resonant frequencies, theidentification frequency associated with each of the remote devicesincluding the plurality of resonant frequencies included in that remotedevice, whereby each remote device may be uniquely identified by theplurality of resonant frequencies.
 8. The method of claim 6 wherein saidstep of actively configuring each of the plurality of remote devicesincludes the step of incorporating a capacitor into each of theplurality of remote devices to provide a resonant frequencycorresponding to the capacitor value.
 9. A method for operating aninductive power supply comprising the steps of: storing a plurality ofidentification profiles and at least one operating parameter associatedwith each identification profile in a memory associated with aninductive power supply; applying inductive power to a remote device atone or more frequencies to determine the identification profile of theremote device contained within the inductive field; comparing thedetermined profile with the stored identification profiles to determinean identity of the remote device; retrieving an operating parameter fromthe memory upon determination of the identity of the remote device; andoperating the inductive power supply in accordance with the retrievedoperating parameter.
 10. The method of claim 9 further including thestep of determining an inherent resonant frequency profile of a remotedevice to determine the identification profile for the remote device.11. The method of claim 9 further including the step of providing aremote device with an identification profile.
 12. The method of claim 11wherein said step of providing a remote device with an identificationprofile includes the step of incorporating an identification capacitorinto the remote device.
 13. The method of claim 11 wherein said step ofproviding a remote device with an identification profile includes thestep of incorporating a plurality of identification capacitors into theremote device.
 14. The method of claim 9 wherein each of theidentification profiles includes one or more resonant frequencies. 15.The method of claim 14 wherein said applying step includes the steps of:applying a pulse of power at the one or more frequencies associated withthe stored profile; and sensing current in the tank circuit to determinewhether the remote device has a resonant frequency at the one or moreapplied frequencies.
 16. A method for securely controlling an inductivepower supply, comprising the steps of: determining a commonidentification profile for remote devices to be powered by the inductivepower supply, the common identification profile including one or moreresonant frequencies; providing each remote device to be powered by theinductive power supply with the common identification profile; applyingan inductive field to a remote device at the one or more resonantfrequencies of the common identification profile; determining whethersaid remote device has a resonant frequency profile corresponding withthe common identification profile; and operating the inductive powersupply to power the remote device if the remote device has a resonantfrequency profile corresponding with the common identification profile.17. The method of claim 16 further including the steps of: providingeach remote device to be powered by the inductive power supply with aunique identification profile; storing the plurality of uniqueidentification profiles and an associated operating parameter in amemory associated with the inductive power supply; once it is determinedthat the remote device has a resonant frequency profile correspondingwith the common identification profile, applying an inductive field tothe remote device at one or more resonant frequencies corresponding toone or more of the unique identification profiles; determining whethersaid remote device has a resonant frequency profile corresponding withone of the unique identification profiles; retrieving the associatedoperating parameter from the memory upon determining that the remotedevice corresponds with one of the unique identification profiles; andfollowing said retrieving step, operating the inductive power supply inaccordance with the retrieved operating parameter to power the remotedevice.
 18. An inductive power supply comprising: inductive fieldgenerating circuitry; frequency control circuitry electrically connectedto said inductive field generating circuitry, said control circuitrycapable of operating said inductive field generating circuitry at aplurality of different frequencies; reflected impedance sensingcircuitry to sense a characteristic of power in the inductive powersupply, said characteristic being indicative of a reflected impedance ofa remote device; identification circuitry to determine an identificationprofile of a remote device as a function of output of said reflectedimpedance sensing circuitry; and power supply control circuitry forsupplying power to the remote device as a function of the identificationprofile of the remote device.
 19. The inductive power supply of claim 18wherein said inductive field generating circuitry includes a tankcircuit having a primary.
 20. The inductive power supply of claim 19wherein said frequency control circuitry includes an oscillator and adriver.
 21. The inductive power supply of claim 20 wherein saidreflected impedance sensing circuitry includes a current sensetransformer coupled to said tank circuit.
 22. The inductive power supplyof claim 21 wherein said identification circuitry includes amicrocontroller and a memory, said memory storing a plurality ofidentification profiles for different remote devices and a plurality ofoperating parameters, each of said operating parameters associated withone or more of the plurality of identification profiles.
 23. Aninductive power supply and remote device combination comprising: aremote device having an identification profile, said identificationprofile including one or more resonant frequencies; and an inductivepower supply having: a driver; a tank circuit having a primary; a sensorin said tank circuit adapted to sense a characteristic of power in saidtank circuit indicative of a reflected impedance of said remote device;identification circuitry to determine said identification profile ofsaid remote device as a function of output of said sensor; and controlcircuitry for controlling operation of said inductive power supply as afunction of said identification profile of said remote device.
 24. Thecombination of claim 23 wherein said inductive power supply includes amemory storing at least one identification profile and at least oneoperating parameter associated with said identification profile.
 25. Thecombination of claim 23 wherein said remote device includes anidentification capacitor.
 26. The combination of claim 23 wherein saididentification profile includes an inherent resonant frequency of saidremote device.